Method for cracking oils in vapor phase



sep1.'4, 1934. P. C. KEITH; JR 1,972,149

METHOD FOR CRACKING OILS IN VAPOR PHASE Filed Dec. 1, 1928 ssheets-Sheet 1 Sept. 4, 1934. P. c. KEITH, JR 1,972,149

METHOD FOR CRACKING OILS IN VAPOR PHASE Filed nec. 1. 1928 ssheets-sheet 2 Sept. 4, 1934. P, c, Kl-:m-l, JR

METHOD Fon cRAcxING oILs 1N VAPOR PHASEl Filed Dec. 1, 1928 3Sheets-Sheet 5 w ws fj/m

- Patented Sept. 4, 1934 l UNITED STATES PATENT; OFFICE METHOD For.cRAcKmG oILs IN varon PHASE Percy C. Keith, Jr., Bernardsvi'lle, N. J.,assigner, by mesne assignments, to Gasoline Products Company, Inc., acorporation of Delaware vApplication December 1, 1928, SerialNo. 323,005

Claims. (Cl. 196-49) This invention relates to the pyrogenesis ofcracking rates of some of the constituents'of petroleum oils and willbe'understood from the. the stock tend to accentuateA the conditionrefollowing description read in conjunction with ferred to above. I havediscovered that a fundathe drawings, in which; mental increase in theeiiiciency of the cracking b Fig. 1 is a diagrammatic representation ofa process maybe obtained by,Vr separating the crackpreferred embodimentof apparatus in which my ing stock into a number of distinct fractionsof processmay be carried out; diiIerent boiling point ranges andthereafter Fig. 2 is a diagrammatic representation of an cracking theindividual fractions so generated. alternative for-m; I prefer to obtainas nearly as possible, having 66 Fig. 3 is a vertical section through aform of regard to the conditions imposed by practice, a apparatus whichmay be employed in conjuncnumber of charging stocks all the constituentstion with my process; of each of which will respond in the same degreeFig. 4 is a cross section taken ai the line 4-4 tothe conditions towhich each of the stocks is of Fig. 3; and subjected. I preferably applyto each such frac- Fig. 5 is a side elevation with parts in section tionthe degree of time, temperature, and/or m of a form ofapparatus employedin conjunction pressure necessary to its optimum conversion into with myprocess and with the apparatus shown desired products. 'I-heseconditions may in any in Figs. 3 and 4. casel be determined bypreliminary tests. Thus,

The pyrogenesis of petroleum oils forproducwhen conditions have beenestablished by such tion of oils of lower boiling point is carried out`tests as to yield the same quantity of desired end by heating crudepetroleum, or such of its disproducts from a series of segregatedfractions as tillatesv as may economically be utilized in this iSObtainable from cracking Conglmrate Stock manner, to cracking'temperatures with or withthe concomitant loss in gas and/or tax-ry orcoky out pressure. The fraction intermediate between materialsisdiminished, or forv an equivalent loss kerosene `and lubricating oilsknown as* gas oil the yield of the desired end products is relatively isfrequently utilized for this purpose because of increased. its lessermarket value, although kerosene, lubri'- My process is applicablegenerally in the pyroeating oil fractions and fuel oils are alsoemgenesis vof petroleum oils toproduce lower boiling ployed at times.The fractions so employed are point oils, as, for example, cracking'toproduce composed of an extended range of compounds as either gas,gasoline, kerosene, gas" oil or lubriindicated by the range of molecularweights and eating oil from stocks of respectively higher boilboilingpoints. The conglomerate of compounds ing point. is subjected tocracking conditions until a certain In the ideal embodiment of myprocess the quantity of material falling within a desired stock issegregated into a plurality of charging boiling range is produced.Simultaneously with stocks of such character that under the conditheformation of this product, or products, mations of heat, time, andpressure imposed, crackterials are produced which do not fall Within ingof the various individual compounds composthe desired range, forexample, when cracking ing the fraction -willtake place at substantiallyto produce a substantial proportion of gasoline the same rate. However,the limitations imwhich is a product composed of a large variety posedby practice require segregation into a of different hydrocarboncompounds, there yis smaller number of stocks than in the idealmethsimultaneously produced a quantity of tarry and od and I thereforesegregate into an appropriate coky materials. Some elements ofaconglomerate number of charging stocks and subject each or stock, forreasons which will ,be given more such stocks to optimum conditions forthe parfully later, require cracking to a degree less than ticularsegregate. 100

others, and because of the fact that the stock I have discovered thatin\ high molecular as' a whole is subjected tothe same conditions weighthydrocarbons of straight chain structure the cracking reaction will becarried too far in the initial-scission on cracking frequently occursthe case :of some of the constituents of the stock adjacent the centerof the molecular chain. In

in order to securev the desired quantity of maone application in myprocess I aim to obtain 105 terlal of a predetermined boiling pointrange and by cracking the products of rst scission of the with theresultant formation of compounds which molecule, and I therefore preparecharging do not fall within'the said range or which are stocks whichupon their initial scission yield deleterious to the operation, forreasonsv which products which fall within the range of physical will bemorefully pointed out. The diierent characteristics of the'materialdesired tobe ob- 110 ceed by dividing my charging stock into a' numberof fractions each of which has a molecular weight substantially twicethat of a constituent of gasoline, then by cracking the stocks to theextent of one scission I obtain a number of products whose molecularweights fall within the range of molecular weights of the constituentsof gasoline. In cases in which the original charging stock containsconstituentsv so heavy that the products of their initial scission willnot fall within the range of physical characteristics of the desiredproducts, these constituents may be separated from the remainder of theoriginal charging stock, as by distillation, and treated in one of twoways; i. e (1) by segregating them from one another as by distillationinto individual fractions and then subjecting each segregated fractionto such conditions as will produce from each segregated fraction aproduct which will yield, upon refractionation, products whichxnay bedecomposed as above into gasoline constituents. 'Ihis procedure enablesme to separate. unsaturated constituents to a degree and to then subjectsuch fractions to appropriate treatment. (2) In view of the limitationsof practice I may subject the entire heavier conglomerate cut tocracking conditions best suited to obtain the maximum yield of productswhich can be segregated into charging stocks of the nature described andcracked in the manner above set forth so as to yield gasolineconstituents.

Alternatively, I may prepare a number of fractions of charging stock,including some which cannot be converted by a single scission adjacentthe center of the molecule into products falling within the desiredrange, and subject each such fraction to the degree of time, temperatureand pressure necessary to its conversion into products of the desiredboiling point range. I may, however, in such cases crack each. suchfraction to yi'eld a cracked material having a position with respect tothe average molecular weightof the series of cracked materials obtainedwhich corresponds to the position held by the parent fraction withrespect to the other members of the parent series. I

In addition to the foregoing I may make a further separation based onchemical characteristics. Thus, I may separate the original crackingstock into two fractions, one containing a preponderance of saturatesand the other containing a preponderance of aromatics and unfsaturates,as, for example, by the application of 55 selective treatmentwith liquid sulphur dioxide. These individual products may thereafter beseparated each into products of different boiling point ranges to beseparately cracked as hereinabove described. Alternatively, thefractions of separate boiling point rangesmay be fr t prepared and eachthereafter separated into fractions of dierent chemical characteristics,as for example, by treatment with liquid sulphur di-l oxide.

' constituents boiling within a different 50 F.

range. 'I'he average molecular weights of these fractions are in someratio to their boiling points, the fraction of relatively high boilingpoint having the highest molecular weight. In cracking these individualfractions conditions are adjusted to produce a series of crackedproducts having the same general relationship. Thus, the fractions oflower average molecular weight will have been cracked to produce acracked material of lower average molecular weight than will have beenproduced from the parent fractions of relatively higher molecularweight. In this way the lighter constituents of the end product gasolinewill have been predominantly produced from those fractions of thecracking stock of lower molecular 'welghti whereas those fractions ofthe gasoline of relatively higher molecular weight will have beenpredominantly produced from the fractions of cracking stock ofrelatively higher molecular Weight.

I achieve a number of distinct advantages by this process, for example,the cracking is carried out on each of the individual cuts underconditions Which may be predetermined in View of the rate ofdissociation of the particular stock to produce the optimum conversion,while the total number of dissociations or the degree of pyrogenesis toproduce any given yield of end product is relatively less than would benecessary with the indiscriminate cracking of a conglomerate stock, andthus the concomitant losses in gas and/or tar or coke are greatlydiminished. A further distinct advantage is that polymerization to formproducts of a greater molecular weight than the parent stock does notoccur to the same degree as when cracking a conglomerate stock. It isunnecessary to carry the cracking reaction on some of the constituentsof the original stock to the point of forming polymers of a characterdeleterious to the operation of the process. Thus, in operating upon aconglomerate stock in the manner used at the present time it may beunavoidable to carry the cracking reaction to the point of third,fourth, fifth or higher scission in thefcase of some of the constituentsof the initial charge and to the scission of polymerized products formedtherefrom in order to obtain the desired yield of the end product.Whereas in my process I prefer to confine the reaction to the formationof the products of scission of a lower order. The scissions off higherorder result in an increase in the products of recomposition, orpolymerization, which contributes to the formation of the products knownas tar and coke.

One of the preferred methods of operating my .process is to crack eachindividual cut of the -cracking stock to produce a cracked materialhaving an average molecular Weight substantially half of that of theparent cut, for example, ranging from to 25% of the averagemolecularweight of the parent cut." In this way, to an extent at least,with a single decomposition of the various molecules composing the gasoil fraction, I am lenabled to convert them into fractions of the of theparticular stock or in view of the particular characteristics of theproduct desired, as, for example, to produce av gasoline having acertain definite proportion of material boiling Within a certainpredetermined range.

The particular method of cracking the individual stocks may be any oneof the methods at present employed or hereafter developed. I may, forexample, crack these individual cuts in either liquid or vapor phase orin a combination of the two and under any degree of pressure. In apreferred embodiment of my invention, however, I subject the individualcuts to a vapor phase cracking of relatively short duration ranging, forexample, from the order of one second up to times of the order of veminutes, at temperatures which may range between 750 and 1500F. and' atpressures which may range from a few atmospheres to partial vacuum. Inthis way I am enabled to effect a carefully controlled dissocia- Vtionof the individual stocks and accurately control the amount ofdissociation applied to each of these stocks so that a large proportionof the individual cuts is subjected to a single dissociation, therebyvautomatically throwing it into the boilingpoint range of the desiredend product with .a minimum production of undesired products. A furtheradvantage of this procedure that I have discovered is that owing to therelatively short times involved, the temperature range in whichcracking`is effected and the low specific volume of the gases in thecracking zon'e, the tendency to polymerization, or reformation ofheavier products, is inhibited, the eiciency of the operation isincreased and I am enabled to diminish the formation oftar and/or coke.

In determining the conditions under which individual cuts of the initialconglomerate charging stock are to be cracked consideration must begiven to the formation of fixed gas. I believe that the theory atpresent held that fixed gas produced by a cracking operation issubstantially produced by the cracking of tar to coke is mistaken andthat in fact such fixed gas is substantially produced by the cracking ofconstituproducts which are extant in the zone of reaction are eitherretained there by reason of the nature of the apparatus which does notpermit of their evacuation immediately upon formation, or are retainedthere by reason of ,their solution in liquid since they are in contactwith large bodies of heavier liquid content inthe system. 'I'his effectis considerably aggravated in many processes by the use of pressure. Itwill be noted that in my improved process because of the nature of theapparatus and the charging stock used there. is substantially no liquidpresent in the system at any time and the apparatus is s'uch thatproducts falling within the gasoline range are removed substantially asquickly as formed. The selection of the temperature bears a definiterelation to the time element'involved in the operation of the apparatus,the more rapid the evacuation of the products from the`zone of reactionthe higher the temperature which may be used, suicient time beingprovided to permit'the reaction to take place. The effect of removingtheE products from the'zone of reaction is to arrest the reaction, andit may be desirable to cool immediately the products removed to preventfurther reaction by reason of the contained heat.

My process will now be described with specic reference to the apparatusdiagrammatically indicated in the drawings. Referring specifically toFig. 1 a cracking stock such as gas oil is passed Y throughthe tubularheater 1, surrounded by the refractory setting 2, and heated by means ofa burner such as 3 communicating with the setting through the port 4.Any alternative means of heating this stock to a temperature of completeor partial vaporization may be employed, such as a heatiexchanger or astill. The partly vaporized cracking stock is delivered through the pipe5 into the fractionating column 6. This column may be suitably insulatedand provided with a number of rectifying .devices such as the customarytransverse partitions carrying down flow pipes and vapor contactingdevices, not shown. The 'design of this column is not a feature of theinvention and any column or corresponding device which is appropriatelydesigned to separate petroleum oil into a number of fractions byrectication may be alternatively employed. Provision is made for takingoff an overhead cut in vapor phase from the column by means of the vaporoutlet 'l and a number of side cuts (ordinarily in liquid phase, butwhich may be inthe vapor phase) from the side outlets 8, 9, 10, 1l, 12,13, 14 and 15. The side cuts may be rectified or stripped in a secondaryrectifying column, if `desired, to eliminate light ends, or,alternatively, any other means for obtaining an enhanced degree ofseparation may be employed. Any bottoms or heavy ends formed in thecolumn ion, by means of the bottom draw-off 15A. The

(column maybe supplied with cooling coils adjacent to the top orintermediate points and with a heating coil adjacent to the bottom orwith re-boiler sections at intermediate points. All

such modifications will be incorporated to the degree necessary toobtain the desired separation of the individual fractions. The cutstaken oi through outlets '7 Vto 15, inclusive, are in view of thenecessities of practice, relatively close cut fractions having, forexample, of constituents boiling Within a 50 F. range, and while theseranges to some extent overlap, the cuts represent a complete series ofcharging stocks, `each of which approaches, within the limits ofcommercial practicability, an ideal charging stock as above defined.This series of ycuts has a range of boiling points and correspondingmolecular weights which increases throughout the series.

These various cuts are passed to individual crackers through controlapparatuses 16 to 23 inclusive which will be hereinafter more fullydescribed, and from the control apparatuses -the cuts pass respectivelyto the individual cracking apparatuses which have been diagrammaticallyindicated by the numerals 24 to 31, inclusive. I

may employany form of cracking apparatus, such as stills which may beadapted to operate under pressure or tubular crackers with or with' outreaction chambers or tubular stills operated in the vapor phase. In anyevent, the cracking i is carried out under conditions which may beascertained in advance by tests tojbe suited to the individual cut.Preferably, when operating to make gasoline the individual cuts arecracked to the parent fraction. I obtain in this way a series of crackedproducts with serially larger molecular Weights corresponding in orderto the molecular weights of the original fractions of cracking stock.The desired end product is therefore obtained by the selective crackingof preferred stocks andwith less actual molecular disruptions andrecombinations than would be incidental to handling a cracking stock asa conglomerate.

For convenience al1 of the cracked materials dis` charged from thecrackers 24 to 31, inclusive, through outlets 32 to 39, inclusive, maybe conducted by means of the manifold 40 into the rectfying column 41which is of suitable construction to permit the separation thereof intothe desired end product, as, for example, gasoline which may be takenoff in vapor phase, if desired, through the outlet 42, and a number ofside cuts taken olf through the side outlets 43 to 50, inclusive. Theseside cuts taken off' through the outlets 43 to 50, inclusive, arepreferably fractionated so that of the constituents of each cut boilWithin a range of 50 F. and will behereinafter more fully considered.The column 6 may be ,operated under any pressure at which appropriatefractionation may be se-- cured, and for purposes of heat economy, ispreferably operated under a pressure in excessv of atmospheric, say, forexample, a pressurenot exceeding 100 pounds per square inch. I achievein this Way the additional advantage that the cuts taken off from theoutlets 8 to 15, inclusive. may, in this manner, be supplied by virtueof A their initial pressure to\the respective cracking apparatuses 24 to31, inclusive. The column 41 may be operated under pressure preferablyless than that obtaining in column 6 so that the progress of materialthrough the entire'system is effected by virtue of the initial pressureobtaining in column 6. The side cuts from column 6 fall within the gasoil range and are such as may, to a large extent, be converted intoconstituents boiling within the gasoline range, particularly where thecracking is so controlled as to produce molecular disruptions occurringat or near the mid-point of the molecule.

The plant illustrated is only an approachto the ideal and somepolymerization may occur to products whose molecular Weight is higherthan those taken off through the side'outlets 8 to 15, inclusive, ofcolumn 6. Such polymerized prod.- ucts are preferably separatelyprocessed as utlined in the preferred manner of processing the cutwithdrawn through 15a, but for commercial reasons may be removed fromcolumn 41 through the side outlet 51 and diverted through pipe 15atopipe 15b to be combined with and processed with the products withdrawnfrom column- 6 through outlet 15a.

The materials delivered through the pipe 15b represent materials whichcannot be converted int-o constituents pf the gasoline series by asingle disruption adjacent the center of the molecule and, while I maysegregate these bottoms by fractionation in the manner described andthereafter crack selectively the individual components and" thenrefractionate and then recrack the individual components fallingwithinhthe gas oil range to gasoline range, I find it sumcient tosubject these components to a mild cracking by forcing the same throughthe tubular heater 52 surrounded, for example, by the refractory setting53 A heated through the port 54 by means of the'burner 55. Thecracking/effected in the heater 52 is not intended to convert the stocktreated thereinpredominately to gasoline, but rather to convert asubstantial proportion of the stock into stocks having `molecularweights approximating those removed from column 6 through the sideoutlets 8 to 15, inclusive. Ihere is of course, the incidentalproduction of a small quantity of gasoline where the operation is notaccurately controlled. 'Ihe stock cracked in this manner is deliveredthrough the outlet 56 into the rectifying column 57, which may be of anysuitable construction, inwhich it is fractionated to form an overheaddistillate, for example, taken off through the outlet 58 whichmayconsist of gasoline and a series of intermediate cuts taken olfthroughthe side outlets 59 to 66, inclusive, which are preferably cut tohave 90% constituents boiling within a range of 50 F. These constituentsboilingwithin the kerosene and gas oil ranges are such as may to a largeextent be converted into constituents of gasoline by a single disruptionoccurring at or adjacent the mid-point of the individual molecule. Anyheavy ends may be taken oir through the side outlet 68, and, while theyare preferably handled by separation and cracking of the individualsegregates, as above outlined,

I 11nd it sufficient in commercialpractice to carry these compounds bymeans of the pipe 69 back into the inlet side of the tubular heater 52for a second cracking operation. Any tarry products-collecting in thebase of the towers 41, 57 and 91 are withdrawn by means of bottomoutlets 50a, 70 and 100a, and diverted from the system. The productsobtained from the side outlets 59 and 66 inclusive, represent productswhich have been cracked and separated into products having a molecularweight approximating those removed from the side outlets on co1- umnsix. As'segregates they are passed through the control apparatusesdiagrammatically indicated by the numerals 'Il to '18, inclusive,discharging into cracking apparatuses 81 .to 88, inclusive, which may beof any suitable construction, although they are preferably of the typehereinafter described. The cuts obtained from tower 41 from the sideoutlets 43 to 50, inclusive, are cuts which have been subjected tocracking and subsequent fractionation. These preferablywillbecrackedinthesamemannerascutsto 15, inclusive, derived from tower6, but for commercial reasons they may be blended with cuts 59 to 66,inclusive, and passed through the crackers 81 to 88, inclusive. Inthe'ideal embodiment of my process all polymerized cuts, even of thesame molecular weight as the cuts 8 to 15, inclusive, will be treatedseparately. This is desirable for two reasons, the first being that thedissociation speed of these polymers may be different than those of 8 to15, inclusive, and further, becauseI have discovered that the presenceof polymerized cuts in contact with undecomposed cuts will enhance theformationof tar.

The cracking accomplished in these cracking apparatuses is conductedunderconditions ascertained by testor experience to be best for theparticular cuts and may be sd adjusted as to produce cracked materialhaving an average molecular'w'eight ranging from 25 to '75% of theaverage molecular vweight of the cut from which the cracked material isderived. In this way a seriesof cracked materials of serially largeraverage molecular weight is produced which have been cracked underconditionsconducive to the maximum emciency, under conditions socontrolled. that the lighter parts of the end product, for example,gasoline, are predominately derived Lorano from the lighter cuts ofcracked stock, whereas the heavier portions of the end product arepredominately derived from the heavier portions of the cracked stock,and under conditions producing the minimum of fixed gas and polymerizedmaterial. The cuts which have been cracked through apparatuses 81 to 88,inclusive, may be ,diverted through the common flow line into therectifying column 91 which may be of any suitable design. From thisrectifying column gasoline may be removed. through outlet 92. From theside of column 91 a series of cuts, shown as 93 to 99a, inclusive, maybe withdrawn and because of .their small quantity may be divertedthrough crackers 81 to 88, inclusive. Itv will be understood that if thepressure in, or the location of, the tower 91 is not such as to causeliquid to now through the lines 93 to 99a, inclusive, into the linesleading to the crackers 81 to 88, inclusive, suitable pumps and checkvalves or other well-known apparatus may be. employed for effecting thispurpose.

The cut 100 may be diverted back to the tubular heater as in the case ofut 51 as is the case likewise with cut 68 from column 57. The cut 68vdiffers from cuts 100 and 51 in that it represents to a large extentproducts which have not been converted into those of the desiredmolecular weight, whereas cuts 51 and 100 are substantially productswhich have been formed by polymerization since the plant shown is onlyan approach to the ideal. For the same reason as before outlined, tarrymatter may be removed through line 100a.

Referring specifically to Fig. 2 which is the diagrammatic elevation ofapparatus adapted to processing crude koil or other petroleum oilscontaining constituents of higher boiling point than gasoline. Thecharging stock is passed through the tubular heater 1 surrounded by .thesuitable refractory' setting 2, heated by means of the burnervdiagrammatically indicated at 3, communicating with the setting throughthe port 4. The crude oil may be heated in heater 1 to a temperature ofsubstantially complete or partial vaporization and is thereafterdischarged through pipe 5 into the rectifying column 6. In the eventthat it is desired to produce` a quantity of gas oil or crackingmaterial in addition to that normally occurring from-the crude,conditions in the tubular heater 1 may be adjusted to produce a crackingeffect, preferably of a moderate character, to convert heavier materialsto a considerable extent into products such as kerosene and' gas oil,which products vare in turn susceptible' to being converted intogasoline by a minimum number of molecular disruptions. This operatio'nis not, of course, conducted under the ideal cracking conditions which Ihave hereinabove described, but is utilized only as a matter ofexpediency. The rectifying column 6 may be of any suitable type.Provision may, for example, be made to take an overhead cut of gasolineby means of the vapor outlet 7 and a series of side cuts from theoutlets 8 to 15, inclusive,and 115 to 118, inclusive. It will, ofcourse, be understood that any alternative number of sidecuts may beemployed, the design in any case being determined by the character ofthe stockto be treated and the number of side cuts which it is desiredto make. Assuming that cuts such as kerosene an'd gas oil are taken offfrom the side outlets 8 to 15, inclusive, these are preferably fairlyclosely fractionated so that 90% of the total constituents of each cutwill boil within a range of say 50 F.

Products evolved from the tower 6 which are heavier than gas oil, or soheavy that they cannot be converted into gasoline to a large extent by asingle disruption adjacent the mid-portion of the molecule, may be takenoff from the column 6 by means of the side outlets 115 to 118,inclusive, combined in the manifold 115a and thereafter treated in thesame manner as the products obtained from the outlet 15a of Fig. l. Anyheavy residue resulting during the operation may be diverted from thesystem by means of the outlet 120.

The several side cuts taken from columns 6 through the side outlets 8 to15, inclusive, may be handled in the identical manner as the side cutstaken from column 6 of Fig. 1 through the side outlets 8 to 15,inclusive, and inasmuch as nthe product taken from column 6 through theside outlets-115 to 118, inclusive, is handled in the identical manneras the products taken from the column 6 in Fig. 1 through the pipe 15a,the subsequent progress of these materials may be ascertained byreference to the previous description relating to Fig. 1 and need not bemore fully illustrated or described.

Referring specifically to Figs. 3 and 4, the form of cracking apparatuswhich I prefer to employ for cracking the individual closelyfractionated cuts which have been described from time to time isdetailed, which apparatus has been designated `for example by numerals24 to 31, inclusive, and 81 to 88, inclusive. This ap' paratus consistsof a refractory setting 150 and -may be heated through the port 151 bymeans vof the burner diagrammatically indicated as 152. A baille wallsuch as 153 may be provided and a down draft section 154 communicatingwith a stack 155. 'I'he tubular heaters 156 and 157 in the down draftsection may comprise a number of tubes through which oil may circulateby means of inlets and outlets 158, 159, 160, 161, respectively, andsections of this character may be utilized for heating or cracking thecuts of relatively wide boiling point correspond- Ving to the operationswhich have been previously described as conducted in tubular heaters 1,52. The walls of the setting 150 are preferably lined with. a number ofrelatively short tubular heaters 162 to 177, inclusive, each of which isadapted to the circulation of hydrocarbon materials by means of inletsand outlets such as 166a and 16612, etc. These'sections are relativelyshort being composed of only a few lengths of tubing adapted to beheated to a large extent by the radiant products of cornbustion evolved.In operation 1 prefer to maintain these heaters 162 to 177, inclusive,at temperatures intermediate between 750 and 1500 F. and to conductcracking operations therein at relatively low pressures ranging from afew atmospheres to sub-atmospheric. The total time of heating of thehydrocarbon gases at these temperatures is preferably limited toa periodranging from one second up to the order of five minutes, whichconditions Il find to favor a symmetrical dissociationvwhich is amenableto control with a simultaneous formation of a relatively small quantityof the products of reassociation or polymerization. In vapor phasecracking apparatus, such'as that shown, I may admix with the petroleumoil undergoing cracking in the vapor phase a material to limit theformation of polymers. I have discovered the formation of polymers isinfluenced, among other things, by the concentration of the-unsaturates1,510

produced by decomposition per unit of space and that this concentrationand consequent polymerization may be inhibited or limited by admixingwith the petroleum oil a substance which does not deleteriously affectthe cracking reaction. In vapor phase reactions I prefer to use amaterial which is gaseous at the temperature of operation, such as afixed gas, steam, carbon dioxide, hydrogen, etc. All. such substanceswhich are not petroleum oils undergoing crack-V ing and which do notdeleteriously affect the` cracking reaction, will be hereinafterreferred to as diluent gases. The cracked and heated hydrocarbonsdelivered through the respective outlets of coils 162 to 177, inclusive,are preferably quenched by cooling them immediately either by contactwith a liquid or a vapor at temperatures below cracking, for example, by

contact with steam or by conducting them I paratus comprises the sideoutlet, such as 8,

carrying a fraction from any one of the rectifying columns hereinabovedescribed, discharging into cracking apparatus such as diagrammaticallyindicated by the numeral 24. A cooling coil such as 200 is connectedinto the outlet 8, preferably adjacent the under side thereof. Thiscoil, controlled by the valve 201, discharges into the pipe 8 at a pointbelow its origin. 'I'her coil 200 may be surrounded by a receptacle,such as 202, through which a cooling fluid is circulated by means ofinlets and outlets, such as 203 and 204, respectively, so that anypetroleum oil, either in liquid or vapor form, passing through the coil200 is automatically cooled and discharged in cooled condition back intopipe 8. By manipulation of the valve 201 the amount of cooled materialwhich is-reintroduced into the pipe 8 may be carefully controlled, andin this way the temperature of the products passing into the crackingapparatus 24 may be controlled, and hence the temperature of theproductsdischarged from` the cracking apparatus 24 may be correspondinglycontrolled. The form of apparatus which I have just described isparticularly adapted to the close control of vapor phase cracking, whichI prefer to conduct in apparatus such as 24 and to which I prefer tosubject the various fractions. into which I separate my originalcracking stock.

It will, of course, be understood that the method and apparatushereinabove specifically described is intended as an illustration of thespecific embodiment of., my inventionand not as a limitation of itsscope. It is my intention that' the invention be limited only by theappended claims in which I have endeavored to claim broadly all inherentnovelty.

1. A continuous. unitary' process of cracking petroleum oils whichcomprises subjecting a cracking stock from a single source to crackingtemperature to effect a primary cracking, subjecting the aresultantcracked 'material to fractionation to form a nal light distillate, aplurality of intermediate condensate fractions and a residue, directlysubjecting the several intermediate fractions, while still hot, toseparate cracking operations in which each fraction is subjected to acracking temperature adapted for the conversion of such fraction toeffect a secondary cracking thereof, combining the resultant hot crackedmaterial from the several secondary cracking operations, subjecting thecombined malterial `to fractionation in another fractionating zone toform an additional'quantity of final light distillate, a plurality ofintermediate condensate fractions adapted' for further cracking and aliquid residue, and preventing the return to, any of said crackingoperations of intermediate condensate from a subsequent fractionatingoperation.

2. A continuous unitary process of cracking petroleum oils whichcomprises subjecting a cracking stock from a single source to crackingtemperature to effect a primary cracking, subjecting the resultantcracked material to fractionation to form a final light distillate, aplurality of intermediate condensate fractions and a heavier fraction,directly subjecting the several intermediate fractions, while still hot,to separate cracking operations in which each fraction is subjected to acracking temperature adapted for the conversion of such fraction toeffect a secondary cracking thereof, combining the resultant hot crackedmaterial from the several secondary cracking operations and subjectingthe combined material to fractionation in a separate fractionating zoneto form an additional quantity of final light distillate, a plurality ofintermediate condensate fractions and a heavier "fraction, passing saidheavier fractions obtained in the fractionation of the products of theprimary and secondary cracking operations immediately through a separatecracking zone and subjecting them therein to cracking temperature toeffect a comparatively light cracking of said heavier fractions, andfractionating the resultant cracked material to separate out anadditional quantity of nal light distillate.

3. A continuous unitary process of cracking petroleum oils whichcomprises subjecting a cracking stock from a single source to crackingtemperature to effect a primary cracking, subjecting the resultantcracked material to fractionation to form a final light distillate, aplurality of intermediate condensate fractions and a heavier fraction,subjecting the several intermediate fractions, while still hot, toseparate cracking operations in which each fraction is subjected to acracking temperature adapted for the conversion of such fraction toeffect a secondaryl cracking thereof, combining the resultant hotcracked material from the several secondary cracking operations andsubjecting it toy fractionation in another fractionating zone to form anadditional quantity of final light distillate, a plurality ofintermediate condensate fractions and a heavier fraction, passing saidheavier fractions obtained in the fractionation of the products of theprimary and secondary ucracking operations, while still hot through aseparate cracking zone and subjecting them therein to crackingtemperature to effect a comparatively light cracking of said heavierfractions, subjecting the resultant products of conversionv of saidheavier fractions to fractionation ina sep#` intermediate condensatefractions and a residue, combining while hot fractions of approximatelythe same boiling point range as obtained in the fractionation of thecracked material formed in said secondary cracking `operation and in thefractionation of the products of cracking said heavier fractions andsubjecting the several composite fractions to cracking temperature toeffect a further cracking of said constituents, and fracof the system,combining the hot products formed in the said several cracking zonesconstituting said one of the successive cracking zones and subjectingthe composite material to fractionation in a fractionating zone toseparate out a final lightdistillate and a plurality of fractions,passmg' said' fractions, while `still not; directly to separate andindividual cracking zones constituting a second successive cracking zoneand subjecting the fractions to cracking temperatures adapted for theconversion of such fractions to effect a further cracking thereof,combining the hot products formed in the said separate and individualcracking zones and subjecting the composite material to fractionation inanother fractionating zone to separate out -a nal light distillate and aplurality of fractions adapted for further cracking.V

5. The continuous unitary process of treating hydrocarbon oils whichcomprises separately cracking a plurality of different oil chargingstocks which have had substantially the same previous heat treatment,combining the resulting hot cracked products, separating the combinedcracked products in a fractionating zone into a f' plurality ofdifferent intermediate fractions and a nal desired distillate, crackingsaid fractions individually while preventing mixtures thereof with saidcharging stocks, and combining the resulting cracked products in asecond fractionating zone, and removing from said second zonea iinaldesired distillate. f

PERCY C KEITH. JR.

